We explore “10 things” that range from the menu of materials available to engineers in their profession to the many mechanical and electrical properties of materials important to their use in various engineering fields. We also discuss the principles behind the manufacturing of those materials.
By the end of the course, you will be able to:
* Recognize the important aspects of the materials used in modern engineering applications,
* Explain the underlying principle of materials science: “structure leads to properties,”
* Identify the role of thermally activated processes in many of these important “things” – as illustrated by the Arrhenius relationship.
* Relate each of these topics to issues that have arisen (or potentially could arise) in your life and work.
If you would like to explore the topic in more depth you may purchase Dr. Shackelford's Textbook:
J.F. Shackelford, Introduction to Materials Science for Engineers, Eighth Edition, Pearson Prentice-Hall, Upper
Saddle River, NJ, 2015

Welcome to week 2! In lesson three we will discover how dislocations at the atomic-level structure of materials explain plastic (permanent) deformation. You will learn to define a linear defect and see how materials deform through dislocation motion. Lesson four compares stress versus strain, and introduces the “Big Four” mechanical properties of elasticity, yield strength, tensile strength, and ductility. You’ll assess what happens beyond the tensile strength of an object. And you’ll learn about a fifth important property – toughness.

講師

James Shackelford

Distinguished Professor Emeritus

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Hello, again. We're back now in Kemper Hall, here on the University of California, Davis campus, and today, we're in the teaching laboratories for the materials science program here at UC Davis, and we're gonna actually have a number of our segments here. In that, this is the laboratory in which we measure a number of important properties, especially mechanical properties, of these materials. And we also will spend some time talking about how we manufacture materials in some simple experiments that illustrate making things fast and slow. Ways in which we're able to understand the nature of microstructures in materials, those maps that tell us what phases are present and how that affects the behavior of these important materials. And then also, how we're able to affect those microstructures and the subsequent properties of the material by a controlled temperature-time history. So we make things slowly, sometimes in equilibrium states and also sometimes very fast in order to affect those properties in advantageous ways. And so now we'll begin with a discussion of atomic structure leading to a particular mechanical property. Remember in our very first thing we talked about how important in material science is the basic concept that structure leads to properties. So this time we're gonna talk about how a particular crystal structure defect at this location is the basis of plastic deformation. [MUSIC] So now, let's talk about the relationship between a particular crystal defect and edge dislocation and an important mechanical property, plastic deformation. So I want to, first of all, define a dislocation, a very specific and simple type, the edge dislocation. And so, let me use a simple model for that. So in this simple stick and ball model, we have a definition of really the simplest type of dislocation or linear defect that is common in structural materials that can lead to plastic deformation. And so, think of this as a very simple example of a metallic crystal structure. And idealistically a simple cubic arrangement of atoms. And what we've done here in this colored area, this blue colored set of atoms in the middle, to highlight the fact that, if you look closely we've squeezed in an extra half plane of atoms and the net result is that the bottom list, the line that defines the bottom of that extra half plane of atoms, is the edge dislocation. Literally the edge of that extra plane. So the idea is that, if we look at a segment of a perfect crystal and make a simple loop around that perfect crystal and come back to the point that we began, and then contrast that with the dislocation area and draw a loop around that, we find that we will not come back to the point of origin, but instead have a closing vector. And that so called Burger's vector is the basis of quantifying this linear structure in a mathematical way. Now, the bottom line of the relationship of this to mechanical performances, the movement of those linear defects, those dislocations, through a crystalline material, is the basis of plastic deformation. And we're gonna look at a video segment that will describe that relationship. Again, as we saw early on in our list of ten things in our very first segment, we talked about how in material science, structure leads to properties. And so, in this very important example of the basis of the plastic forming, especially metallic structural materials, it's this linear defect that provides that defamation.